The present invention relates to an air conditioner, and more particularly, to an air conditioner with a refrigeration cycle including a thermal storage tank.
Recently, air conditioners have been developed which have a refrigeration cycle including a thermal storage tank. In one such conventional air conditioner, the thermal storage tank is connected to the discharge side of a variable-capacity compressor, which is driven by means of an inverter unit. A regenerative material is sealed in the storage tank. It serves to exchange heat with a refrigerant discharged from the compressor. The storage tank is connected in succession with an indoor heat exchanger, an expansion device, an outdoor heat exchanger, and the compressor, all these members constituting the refrigeration cycle. The regenerative material in the thermal storage tank is heated and stored with heat by the refrigerant discharged from the compressor. The compressor is driven with fans of the indoor and outdoor heat exchangers off and on, respectively. Thereupon, the high-temperature, high-pressure refrigerant condenses in the storage tank, and its condensation heat is stored in the regenerative material.
The heat stored in the thermal storage tank is utilized as a heat source for heating the refrigerant, at the start of the heating operation of the refrigeration cycle or during the defrosting operation thereof.
Conventionally, in the regenerating operation described above, the compressor is driven within the same output frequency range as in an ordinary heating operation. In this case, however, the condensation pressure of the refrigerant increases drastically in the thermal storage tank, thereby entailing various problems. More specifically, paraffin or other material is used usually as the regenerative material which utilizes latent heat. At the start of the regenerating operation of the refrigerating cycle, the regenerative material is in a solid phase, so that its heat transfer rate is low, and its effectiveness is lower than that of the indoor heat exchanger or the like. Accordingly, the high-temperature, high-pressure refrigerant discharged from the compressor is kept at high pressure without being fully condensed in the storage tank. The inverter unit cannot rapidly control the output frequency of the compressor in accordance with the high-pressure state of the refrigerant. Thus, the compressor may possibly be damaged by an excessive increase of pressure, or stopped by an actuation of a condensation-temperature sensor which is provided beside the indoor heat exchanger.
Usually, moreover, the compressor requires a protection time of several minutes before restarting. In the regenerating operation, therefore, the compressor cannot operate satisfactorily, thus lowering its operating efficiency considerably.